The present invention generally relates to the field of ventilation duct systems, and in particular to the manufacture of helically-wound lock-seam tubes having air nozzles.
Ventilation ducts of this general type are disclosed in a pamphlet entitled xe2x80x9cACTIVENTxe2x80x94The Active Thermal Displacement Ventilation Systemxe2x80x9d issued by the Finnish company ABB Flxc3xa4kt Oy in 1995. This known ventilation duct system, referred to as the ACTIVENT system in the following, includes tubes helically formed from a sheet metal strip and having small air nozzles extending through the tube wall and distributed in a helical pattern. Such a tube is shown under the subtitle xe2x80x9cFittingsxe2x80x9d on page 9 of the above pamphlet.
As is shown on page 2 of the pamphlet, the air nozzles of the tubes of the ACTIVENT system are adapted to evenly distribute air along the entire length of the duct. Secondary air outside the tubes is mixed with the air flowing out of the nozzles to establish the above-mentioned thermal displacement. Systems like this produce a good cooling effect without disturbing draught and they use less supply air than traditional systems.
In the pamphlet, there is no disclosure whatsoever of how the tubes of the ACTIVENT system are manufactured.
It should be mentioned, however, that ventilation tubes like these may be manufactured by means of a so-called tube former, for instance of the general type which is disclosed in the patent U.S. Pat. No. 3,546,910 issued in 1970 and entitled xe2x80x9cLock-seam helical tubingxe2x80x9d. Tubes produced by means of this known machine are called xe2x80x9cSpiro Rib Tubesxe2x80x9d.
The present invention aims at providing a technique by means of which helically-wound lock-seam tubes, which are of the basic type mentioned, can be manufactured in a modern and effective manner.
According to the invention, this aim is fulfilled by a method of manufacturing a helically-wound lock-seam tube intended for a ventilation duct system and having a plurality of air nozzles through its wall. The method comprises the steps of:
a) feeding a strip of sheet metal from a supply to a punching and pressing unit;
b) punching and pressing said strip in said punching/pressing unit to form at least one longitudinal row of spaced openings through said strip, each of said openings being defined by a collar formed of strip material and projecting from one surface of said strip;
c) feeding said punched strip to a roller unit, in which at least one longitudinal bead is formed in said strip in parallel with said at least one row of openings;
d) feeding said punched and beaded strip to a forming head in which said strip is helically wound to form a tube having a helical lock seam, wherein each helical turn of said tube has at least one row of spaced openings forming said air nozzles projecting radially out of said tube wall;
e) feeding said helically-wound lock-seam tube out of said forming head; and
f) cutting said tube into desired lengths.
The aim of the invention is also fulfilled by an apparatus for manufacturing a helically-wound lock-seam tube intended for a ventilation duct system and having a plurality of air nozzles through its wall. The apparatus comprises:
a) a supply of a sheet metal strip;
b) a punching/pressing unit for punching and pressing said strip fed from said supply to form at least one longitudinal row of spaced openings through said strip, each of said openings being defined by a collar formed of strip material and projecting from one surface of said strip;
c) a roller unit for rolling said punched strip fed from said punching/pressing unit to form at least one longitudinal bead in said strip in parallel with said at least one row of openings;
d) a forming head for forming said punched and beaded strip to a helically-wound lock-seam tube, wherein in each helical turn of said tube has at least one row of spaced openings forming said air nozzles projecting radially out of said tube wall;
e) means for feeding said helically-wound lock-seam tube out of said forming head; and
f) means for cutting said tube into desired lengths.
Further, the aim of the invention is fulfilled by a helically-wound lock-seam tube for a ventilation duct system, said tube having a plurality of air nozzles through its wall and being formed from a sheet metal strip helically formed in helical turns defined by a helical lock seam, wherein each helical turn of said tube comprises at least one row of spaced openings forming said plurality of air nozzles projecting radially out of said tube wall, and wherein each helical turn of said strip further comprises a helical bead formed in said strip in parallel with said at least one row of spaced openings forming said air nozzles.
The invention gives several advantages. By the technique suggested, tubes of the present type may be manufactured in line and easily cut into desired lengths. When the tube diameter is to be changed, normally by replacing the forming head, the parameters related to the tube diameter are easily adjustable. For instance, the operation of the punching and pressing unit is easy to adjust so that the positioning of the openings to be punched, which will form the air nozzles of the finished tube, is adjusted to the new tube diameter.
In a preferred embodiment, the punching/pressing unit comprises two members, one of which is displaceable with respect to the other in order to punch a first row of openings which are offset relative to a second row of openings, the openings of these rows being more or less offset with respect to each other. By adjustment of the displaceable punching/pressing member, the positioning of the two rows of openings may be adjusted in such a manner that the air nozzles of the finished tube are arranged in axial rows parallel with the center axis of the tube. Further, it is preferred that the bead to be formed in the following roller unit is positioned between and two rows of openings.
Preferably, the punching/pressing unit may operate both continuously and intermittently. In the first case, the air nozzles will be equidistantly spaced in a helical row throughout the tube, whereas in the second case the finished tube will have at least one axially extending surface that has no air nozzles. By operating the punching/pressing unit continuously or intermittently, various air nozzle patterns may easily be provided on the finished tube, such as 360xc2x0, 270xc2x0, 180xc2x0, 90xc2x0 and two times 90xc2x0 around the periphery of the tube. The operation of the punching/pressing unit is controlled by means of a computer in which various nozzle patterns may be programmed.
In still another preferred embodiment, the angle between the center axis of the tube and the strip feeding direction in the roller unit is adjustable in accordance with the diameter of the tube, so that the strip feeding direction between the strip output of the punching/pressing unit and the strip intake of the roller unit is maintained straight, which ensures secure in-line production conditions. Most preferably, the forming head is mounted on a base member which is turnable about a vertical axis, whereas the roller unit is stationary.
The inventive tube is advantageous since it has a greater number of air nozzles per unit of length than prior-art tubes of similar type. This enhances the air distribution from the tube and in the room. The structure of the tube is compact, since each helical turn has at least one row of air nozzles as well as a helical bead.
The bead provided in the roller unit gives special advantages. First, the helical bead on the tube generally has an important stiffening effect. Second, the helical bead protects the air nozzles during handling and transportation of the tube, since the bead preferably projects further radially out of the tube than the air nozzles. Third, the helical bead which preferably is positioned between two parallel rows of air nozzles, has a damping effect on the noise caused by the air flow out of the nozzles.
Preferably, the forming head is of the type in which the tube is formed within an annular body having internal grooves receiving the bead and the air nozzles projecting radially outwards from one surface of the strip which is being formed in the forming head. Owing to this forming head structure, smooth forming of the tube is accomplished, and the bead and the air nozzles do not interfere with the inside surface of the forming head.